1. Field of Invention
The present invention relates to a device for attaching boom assemblies ("wishbones") to masts on sailboards or similar wind-powered vehicles.
2. Description of Prior Art
On a sailboard, a "wishbone" is a device for stretching the sail away from the mast into an aerodynamic shape. The boardsailor manipulates the wishbone to control the position and orientation of the sail and mast relative to the sailboard.
The wishbone generally consists of a front fitting and a rear fitting connected by two booms. Sometimes boom extension pieces are inserted between the booms and the rear fitting. The wishbone is usually attached to the mast by lashing its front fitting to the mast with a piece of line called an inhaul. The combination of front fitting and inhaul can be referred to as a "gooseneck," a term commonly applied to the fitting that attaches the boom to the mast on a conventional sailboat. The present invention, which replaces both the front fitting and the inhaul, and which is used only with a wishbone, can be referred to as a "wishbone gooseneck."
The attachment of wishbone to mast must resist any motion of the wishbone along the mast. It must also resist the tendency of the wishbone to rotate about its longitudinal axis as torque is applied to it when the boardsailor hangs from one of the booms.
Yet the wishbone should be attachable to the mast over a range of positions along the mast. It is also desirable that neither attaching nor detaching the wishbone and mast require great strength or dexterity.
A common method of attachment involves wrapping the inhaul around the mast several times and tying both ends of the inhaul to the front fitting. This is done with the wishbone roughly parallel to the mast. Subsequent rotation of the wishbone so that it is perpendicular to the mast stretches the inhaul and tightens this connection. If the inhaul was lashed tightly enough to begin with, the connection will now be tight enough so that the attachment is adequately rigid, until the inhaul either loosens or stretches. If the inhaul was lashed too tightly to begin with, rotating the wishbone to the perpendicular position can crush the mast, in part because the contact between the mast and the front fitting is insufficiently distributed. It is often difficult to untie the inhaul, for its knots tighten under use; yet it must be untied when detaching the boom and the mast or when adjusting the position of the boom on the mast.
Known in the art are several devices that provide simpler operation than do lashed inhauls.
U.S. Pat. No. 4,587,916 to Guerette (1986) shows a device in which the inhaul is replaced by a lever-operated, hook-clamping strap, which holds the mast against the crotch of a V-shaped front fitting. U.S. Pat. No. 4,424,759 to Dolence (1984) shows a device in which rotation of the wishbone compresses a split collar onto the mast. U.S. Pat. No. 4,679,518 to Frank (1987) shows a device in which rotation of a screw member deforms a split collar so that it clamps onto the mast. The devices of Guerette, Dolance, and Frank all tend to lessen their grip on the mast as outhaul tension is increased and the sail tends to pull the mast aft with respect to the device. This is because the strap or collar containing the mast tends to elongate fore and aft.
U.S. Pat. No. 4,674,428 to Weber et al. (1987) shows a front fitting consisting of a rigid split sleeve with a friction-reducing lining. This device grips the mast poorly if at all with the application of outhaul tension, because the split collar is rigid rather than flexible, and because of the friction-reducing lining. This device, as well as those of Guerrette, Dolance, and Frank, will deform under torsional loading, because they do not surround the mast with structural material capable of resisting such deformation. Under the loading of a boardsailor hanging from one of the booms, the uppper surfaces of Weber's split sleeve 90, Guerrette's strap 49, Dolance's mast collar 15, and Frank's clamping jaws 13 will no longer be planar; rather, these upper surfaces will assume the shape of the upper surface of a split lockwasher. This deformation permits the wishbone to rotate about its longitudinal axis, reducing the boardsailor's control over the position and orientation of the sail.
A device marketed under the trademark SURFCAT PRO SPORT (source unknown) utilizes a split collar clamped to the mast with five bolts and nuts. On the front of this split collar is a short horizontal bar connected to the collar by two vertical lugs. This bar mates with a hook connected to a V-shaped front fitting, the rear face of which closely conforms to the collar as the boom is rotated from parallel to the mast to perpendicular to it.
A device marketed under the trademark LINK (source unknown) consists of two hollow half-cylindrical pieces that are clamped to the mast by the rotation from vertical to horizontal of two hollow cylinders, connected to the front ends of the booms, about a horizontal shaft forward of the half-cylindrical pieces. Its clamping force is diminished, rather than fostered, by outhaul tension; outhaul tension deforms the wishbone so that it becomes shorter and wider, and increases the acute angle between the forward ends of the boom pieces, which decreases their clamping force on the mast.